We’ve been working through a number of M96 and M97 engines lately and wanted to share some observations that may help owners make sense of bore scoring - what’s serious, what’s cosmetic, and how to read a borescope correctly.

After opening up well over 100 engines over the years, we noticed some patterns that might help clear up confusion:

• The correct way to borescope is through the spark-plug holes - not from the bottom.
  
• A borescope almost always looks worse than reality; light and shadow can exaggerate marks.
  
• Vertical lines are normal machining traces. True scoring shows depth and shadow movement.
  
• Some deep grooves come from debris, not piston-wall failure.
  
• Most “scary” images we see online turn out to be surface scuffing with no measurable depth once torn down.
  
• Scoping from the top at bottom-dead-center shows more than 75 % of the bore surface anyway.
  

We put together a technical walkthrough to show real images, side-by-side borescope vs. teardown, and some guidance for interpreting what you’re seeing.
The goal isn’t to sell anything, it’s simply to share what’s been learned from hands-on inspection of these engines and hopefully demystify a topic that causes a lot of unnecessary worry.

🔗 Video link: If you find it useful, feel free to discuss your own observations or experiences below.

 

My question is what does scoping an engine do for someone that already owns the car? What if I scoped my engine and I saw what you saw in the video? Is there anything that you would change with regards to the continued running of the engine?

Edit: I have never scoped or thought I needed to scope my engine.

 

It certainly is nice to hear an alternate rational analysis from a highly regarded engine builder. He certainly has a financial incentive to jump on and promote the doom and gloom hype train but chose to not do it. Less expensive PPIs with bore score checks through the spark plug holes are welcomed.

 

I’m wondering the same thing as I never did the bore scope when I did the PPI 4 years ago when I bought the car. I have been doing UOA religiously, is that enough peace of mind? Here’s my latest one:

 

Where in the cylinder does bore scoring start? What is the root cause of scoring?

If I'm buying one of these cars at full price where the engine will cost $25K or more to rebuild, I want to know it has zero scoring. If it starts above the piston at BDC, then I'm good with scoping from the top. But if it starts below the top of the piston at BDC, then I want to scope from the bottom with the piston at TDC. So, where does scoring start? That's where I want to inspect.

 

Quite frankly I dont see a reason why you wouldn't want to scope the bores to see what shape they are in. Its a low cost procedure.

1. If they are in ****ty shape, then you know you have a rebuild coming and should plan accordingly.

2. If bore scoring has started but not bad, you can plan accordingly with what procedures you want to take to slow it down so you have breathing room for your next steps.

3. If they are great shape, then you dont have to worry about a rebuild and can spend your money refreshing/upgrading other parts on a 21-26 year old car.

For sure, plenty of owners and prospective owners just dont think its necessary to scope the bores for many reasons.

1. They don't plan on being a long-term owner.

2. They have incredible DIY skills and plan on rebuilding the engine to the latest and greatest at anytime when needed.

3. They already have a pile of cash that they plan on spending on a professional rebuild to boost the output of an already incredible chassis asap.

4. Other

No right or wrong answer. Just plenty of paths an owner or prospective owner can go down depending on what their preferences are.

 

That's certainly the proof in why you do repeated UOAs. Trend data. I don't see any change in AL or SI levels, so if a bore scope was clean and all subsequent samples are roughly the same, that you don't have a problem.

The fuel % is a calculated figure with BS, so you have to take that with a grain of salt. But if you see that go up over 1%, I'd start looking for injector issues that would lead to bore wash down.

 

Thank you for the feedback. I haven't done a bore scope yet, so right now I'm going to continue monitoring all the vitals regularly.